The technology disclosed herein generally relates to methods for splicing two optical fibers together and, more particularly, relates to splicing two plastic optical fibers. As used herein, the term “splicing” means optically coupling the end faces of two optical fibers so that light emitted by one fiber is received by the other fiber.
An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis. The fiber consists of a transparent core surrounded by a transparent cladding layer (hereinafter “cladding”), both of which are made of dielectric materials. Light is kept in the core by the phenomenon of total internal reflection. To confine the optical signal in the core, the refractive index of the core is greater than that of the cladding. The boundary between the core and cladding may either be abrupt, as in step-index fiber, or gradual, as in graded-index fiber.
An important aspect of a fiber optic communication is that of connecting two fiber optic cables such that optical loss is minimized. Temporary or semi-permanent connections are made by means of specialized optical fiber connectors. It is often necessary to align an optical fiber with another optical fiber. This can involve either carefully aligning the fiber and placing it in contact with the device, or using a lens to allow optical coupling. In some cases the end of the fiber is polished into a curved form that makes it act as a lens.
A plastic optical fiber (POF) is an optical fiber that is made of polymeric materials. Similar to glass optical fiber, POF transmits light (for illumination or data) through the core of the fiber. Its chief advantage over the glass product, other aspects being equal, is its robustness under bending and stretching. Typically, the core is made of poly(methyl methacrylate) (PMMA) or polystyrene, while the cladding is made of fluorinated polymer.
Plastic optical fiber can be substituted for heavy and bulky copper conductors in an airplane data bus network. However, it is not uncommon for a plastic optical fiber to break during the complex airplane wiring process. A splice provides a quick repair of broken plastic optical fibers in the airplane wiring process.
Currently there is no commercial-off-the-shelf avionics-grade POF splice that is designed for a rugged avionics environment. Commercially available POF splice techniques use epoxy to join the two POF end faces. Joining the two end faces with epoxy is not very durable because bulk epoxy will soften at high temperature, thereby increasing the optical loss of the POF in the splice. The pull strength of the splice will be reduced at high temperature using the existing commercial POF splicing technique. The commercial POF splice does not address the issue of end-face damage due to a high-vibration environment. In addition, the use of epoxy requires ultraviolet light or heat for curing. This is not a preferred process to use during the wiring installation in a commercial airplane.
The well-established glass optical fiber fusion splicing technique using high-temperature arcing at the fiber end faces is not applicable to POF because of the material and fiber diameter differences. POF will melt instantly when arcing heat is applied at the POF end faces.